FIG. 1 illustrates a prior art mathematical model for channel separation in "matrix" multichannel encode-decode systems as first described by the present inventor in "Analyzing Phase-Amplitude Matrices", Journal of the Audio Engineering Society, Vol. 19, No. 10, p. 835 (November 1971). This model is referred to as "Scheiber's Sphere" in "The Subjective Performance of Various Quadraphonic Matrix Systems", Report RD 1974/29 (1974, British Broadcasting Corporation, Research Department). In this model, two times the arc tangent of the amplitude ratio with which a signal is applied to/recovered from a pair of transmission or storage channels (respective "A" and "B" or "L.sub.T " and "R.sub.T ") determines the apparent angular position, .alpha., of a sound source in a horizontal "amplitude plane." The phase difference with which the signal is applied to/recovered from the pair of channels comprises the apparent angular position, .beta., of the sound source in a vertical "phase plane." Decoded separation between encoded/decoded signals, or "channel separation," is a function of spherical angular separation between the spherical .alpha.,.beta. coordinates of decoding and those of encoding, becoming infinite for any encode/decode pair of signals having 180.degree. spherical angular separation (decoding coordinates diametrically opposed to encoding coordinates). The above-referenced article "Analyzing Phase-Amplitude Matrices" sets forth this theory more fully, and is incorporated herein by reference.